Despite advances in surgical instruments, and despite advances in the level of skill possessed by surgeons, procedures such as laparoscopy, endoscopy and the like are still plagued by significant disadvantages in comparison to traditional open surgical procedures. One of these disadvantages is the relatively lengthy operative times needed to perform laparoscopic and endoscopic procedures. A factor contributing significantly to such relatively long operative times is the lack of a laparoscopic instrument for safely and effectively performing rapid blunt-tissue dissection. Blunt-tissue dissection includes the separation of tissues such as tumor sacs or membranes from surrounding healthy tissue.
Numerous instruments exist for performing blunt tissue dissection in open surgical procedures. Such instruments are most often held in the hand of the surgeon and typically include a cutting and/or nudging apparatus which must actually contact the tissue to be separated. Such instruments have also included vibrating heads, physical nudging apparatus or scalpels. Unfortunately, the use of ultrasonic vibrating heads often entails the use of cumbersome umbilical connections to nearby generators (generally large enough to be floor mounted) with electrical power inputs of which such equipment can be very expensive. Alternatively, the use of scalpels can cause undesired damage to and bleeding from the tissue being separated. Moreover, the use of these and other instruments has required an extreme degree of care, and patience and delicate manipulation are necessary in their use if trauma to the patient is to be minimized. These problems are multiplied by the restricted movement and limited visibility encountered during laparoscopy, endoscopy and similar closed procedures.
Other problems exist with dissection techniques used in laparoscopy, endoscopy and the like. Laparoscopic graspers and scissors can be used to identify a target tissue plane and to separate the desired structure from tissues such as surrounding fat and overlying fascia. Because such instruments are rigid, because they generally develop tissue planes slowly and because they provide relatively poor tactile feedback (such tactile feedback is often referred to as "feel"), their use can result in the inadvertent creation of false tissue planes. Moreover, the natural tissue planes are sometimes not recognized. The result is the possibility that the surgeon can become disoriented during the procedure, and unintentionally damage non-targeted organs or tissue.
Some of these drawbacks can be overcome by the use of hydrodissection. Hydrodissection uses a pressurized fluid (such as water or saline solution), typically at about 700 mm Hg (roughly about 1 atm), to develop natural tissue planes. A jet of pressurized fluid moves along the path of least resistance through the tissue with relatively little trauma to the surrounding tissue and structures. Once the natural tissue planes are developed, conventional laparoscopic graspers and scissors are used to complete the procedure. Hydrodissection, however, has several limitations, including an undesirably low dissecting pressure, the creation of fluid laden tissues, the pooling of fluid in the insufflated cavity in the patient and the need to periodically evacuate the pooled dissecting fluid. The suctioning of pooled dissecting fluid from the insufflated cavity may, of course, result in the partial or total collapse of the insufflated cavity, if not carried out carefully. Such suctioning, of course, adds to the time required for performing the procedure, and draws the attention of the surgeon from the procedure itself.
The use of devices including electrosurgical cutters or lasers for tissue dissection is also subject to many of these drawbacks. Some of these devices require irrigation during use, so that the problem of the pooling of fluid remains. Moreover, such devices often produce smoke during their use, which interferes with the surgeon's view of the operative cavity, and which (like dissecting fluid) must be suctioned from the cavity.
Pressurized gas has been used to separate animal tissues, for example, for assisting in the skinning of an animal. U.S. Pat. No. 4,118,830 (Weiland, Oct. 10, 1978) discloses a hand-held device for this purpose. It has also been suggested to use pressurized gas for the surgical separation of tissues. For example, U.S. Pat. No. 4,357,940 (Muller, Nov. 9, 1982), U.S. Pat. No. 4,709,697 (Muller, Dec. 1, 1987) and U.S. Pat. No. 5,022,414 (Muller, Jun. 11, 1991) are all directed to a pneumatic tissue separator and method for using the same which includes a floating tip, through and/or around which gas (such as medical grade carbon dioxide) or liquid may be passed in order to separate tissue or clear previously separated tissue. The last of these patents notes in passing (at column 13, lines 36-44) that the device disclosed in it can be used as an adjunct in endoscopy, bronchoscopy, proctoscopy, sigmoidoscopy or arthroscopy. However, none of these patents discloses or suggests either the recognition of or the solution of a significant problem which may arise during the use of a pneumatic tissue separator in an insufflated cavity, in particular, the undesirable increase in cavity pressure which results from the introduction of the dissecting gas into the cavity.
It has been noted that this rise in pressure in the cavity, for example, a rise in intraperitoneal pressure, can be rapid; M. S. Pearle et al., "Laparoscopic Pneumodissection: Results in Initial 20 Patients," J. Amer. Coll. Surg., 1997; 184:579-83. The article notes that intraperitoneal pressure can be maintained at 15 mm Hg or less by intermittent desufflation through the side arm of a laparoscopic port. Such a release of pressure can be rapid as well; M. S. Pearle et al., "Laparoscopic Pneumodissection: Initial Clinical Experience," Urology, 1995; 45:882-85. Unfortunately, the need to continually monitor cavity pressure and the need to manually release excess pressure through a laparoscopic port side arm can undesirably draw the attention of the surgeon away from the procedure being performed. It has been suggested that positioning an available pop off valve in line with the insufflation tubing, attached to the side arm of the port, can achieve this same purpose; S. M. Gardner et al., "Laparoscopic Pneumodissection: A Unique Means of Tissue Dissection," J. Urol., 1995; 154:591-94. Such a valve would open whenever the cavity pressure, for example, the intraabdominal pressure, exceeded 16 mm Hg. The use of such a valve could be expected to have several drawbacks, however. The positioning of the valve in the side arm of a laparoscopic port prevents the side arm from being used for other purposes. Essentially, this requires the perforation of the patient with an additional laparoscopic sheath. It is of course highly desirable that a minimum number of sheaths be used during laparoscopic and endoscopic procedures. Moreover, pop off valves and the like are subject to failure and significant variations in operating tolerance, and can be stuck closed at pressures higher than intended. Further, it may take a small but perhaps appreciable time for pressures at different locations within the insufflated cavity to equalize, especially in a dead end structure such as a port side arm. This might undesirably delay release of pressure at the pop off valve. Of greatest concern may be that intracavital pressure cycles up and down between actuations of the pop off valve, with a resultant cyclic variation in the volume of the insufflated cavity. This not only distracts the surgeon but may cause relative movement of other operative instruments.
It would be highly desirable to have a tissue dissector which reliably prevented the build up of pressure in an insufflated surgical cavity. It would also be highly desirable to have a tissue dissector which achieved this prevention automatically, without requiring the attention of the surgeon to either continuous monitoring or to manual pressure release. It would also be desirable to have a tissue dissector which achieved higher dissection pressures than obtained with hydrodissection, yet which avoided the need to suction liquid or smoke from an insufflated surgical cavity. It would further be highly desirable to have a tissue dissector which did not risk trauma to visceral organs or blood vessels during normal use, as is possible with lasers, scalpels and other cutting devices. Of course, it should go without saying that it would also be desirable to achieve these objects at a relatively low cost, in particular, while avoiding the expensive equipment costs associated with ultrasonic cutters.